X-ray localizer light system

ABSTRACT

An X-ray localizer light system comprises: a long life X-ray localizer light source; an optical concentrator, the light source being situated at a first focal spot, the optical concentrator being configured for concentrating X-ray localizer light from the light source to a second focal spot; and an opaque shield having an aperture therein situated proximate to the second focal spot and being of such a geometrical shape so as to maximize light throughput while meeting light field edge contrast requirements. In another light system, the optical concentrator comprises a reflector comprising a quasi-ellipsoidal portion within which the light source is situated, a cylindrical portion situated between the quasi-ellipsoidal portion and the shield for reflecting stray light, a back reflector portion situated proximate to the shield, and a centrally-mounted portion situated between the aperture and the light source for directing back-reflected light in the direction of the aperture.

BACKGROUND OF INVENTION

The invention relates generally to X-ray localizer light for visualmarking of a target area to be exposed to X-rays.

An X-ray system typically includes a collimator for establishing anexposure area to the X-rays. The collimator typically includes two pairsof blades made of X-ray absorbing material, such as lead, which can beopened and closed to establish the X-ray exposure area. Because theX-ray beam is not visible to the eye, an X-ray localizer light system istypically provided for supplying visible light from a lamp to visuallyindicate the exposure area. To accurately represent the area of X-rayexposure at all distances from the collimator, the light and X-raysources are positioned at substantially the same respective distances toat least three points on a flat optical mirror which are not in astraight line and which cause the visible light to be coincident withthe X-rays. Thus, the light source does not have to be in the path ofthe X-ray beam.

Precise alignment of the distance to the light source and the angle ofthe mirror are important to achieve coincidence of edges of the visiblelight and X-ray exposure areas. The primary challenge with conventionalapproaches has been adequate illumination with satisfactory edgecontrast associated with the collimator blades.

Low voltage quartz-halogen projector lamps with high filamenttemperatures have been used. Such projector lamps have relatively smallfilament size and high lumen output (e.g., 5000 lumens), offeringadequate edge contrast and illumination at the target area. Theseprojector lamps typically also withstand repetitive on/off switching andcost significantly less than high intensity discharge (HID) lamps.However, due to the inherent tradeoff between lumen output and filamentlife in halogen lamps, these projector lamps typically have very shortlife (about 300 burn hours or less).

In X-ray collimator applications, lamp replacement involves preciseoptical alignment and is a task performed by a qualified servicetechnician. The more frequently that a lamp needs to be replaced, thehigher the incidence of down-time and labor costs.

It would therefore be desirable to improve localizer lamp life in X-raycollimator applications while maintaining or exceeding conventionalperformance characteristics of localizer light systems.

SUMMARY OF INVENTION

Briefly, in accordance with one embodiment of the present invention, anX-ray localizer light system comprises: a long life X-ray localizerlight source; an optical concentrator, the light source being situatedat a first focal spot, the optical concentrator being configured forconcentrating X-ray localizer light from the light source to a secondfocal spot; and an opaque shield having an aperture therein, theaperture being situated proximate to the second focal spot and being ofsuch a geometrical shape so as to maximize light throughput whilemeeting light field edge contrast requirements of the X-ray localizersystem.

In accordance with another embodiment of the present invention, a lightsystem comprises: a light source; a reflector having first and secondfocal spots, the light source being situated at the first focal spot,the reflector being configured for concentrating X-ray localizer lightfrom the light source to the second focal spot; an opaque shield havingan aperture therein, the aperture being situated proximate to the secondfocal spot, wherein the reflector comprises a quasi-ellipsoidal portion,wherein the light source is situated within the quasi-ellipsoidalportion, a cylindrical portion situated between the quasi-ellipsoidalportion and the shield for reflecting stray light from thequasi-ellipsoidal portion in the direction of the shield, a backreflector portion situated proximate to the shield, and acentrally-mounted portion situated between the aperture and the lightsource for directing back-reflected light in the direction of theaperture.

BRIEF DESCRIPTION OF DRAWINGS

These and other features, aspects, and advantages of the presentinvention will become better understood when the following detaileddescription is read with reference to the accompanying drawings in whichlike characters represent like parts throughout the drawings, wherein:

FIG. 1 is schematic diagram of an X-ray localizer light system inaccordance with one embodiment of the present invention.

FIG. 2 is a sectional side view of the X-ray localizer light system ofFIG. 1 in accordance with another more specific embodiment of thepresent invention.

FIG. 3 is a sectional side view of a light system in accordance withanother embodiment of the present invention.

FIG. 4 is sectional side view of a more specific embodiment of adiffuser and shield arrangement for use in another more specificembodiment of the present invention; and

FIGS. 5 and 6 illustrate aperture shapes for use in several morespecific embodiments of the present invention.

DETAILED DESCRIPTION

FIG. 1 is schematic diagram of an X-ray localizer (visualization) lightsystem 1. In accordance with one embodiment of the present invention anX-ray localizer light system comprises: a long life X-ray localizerlight source 10; an optical concentrator 11, light source 10 beingsituated at a first focal spot F1, optical concentrator 11 beingconfigured for concentrating X-ray localizer light from light source 10to a second focal spot F2; and an opaque shield 14 having an aperture 16therein, aperture 16 being situated proximate to second focal spot F2and being of such a geometrical shape so as to maximize light throughputwhile meeting light field edge contrast requirements of X-ray localizerlight system 1. In a typical X-ray environment, such as a medical systemor an industrial system X-ray environment, for example, X-ray source 18directs X-rays through collimator 22 to a target area 24. One or moremirrors 20 are typically used to direct the light from X-ray localizerlight system 1 to target area 24.

FIG. 2 is a sectional side view of a more specific embodiment of theX-ray localizer light system of FIG. 1. Typically light source 10includes a light emitting element 32 surrounded by a light bulb 34.Because light emitting element 32 (typically a filament, for example) isbright and close to light bulb 34, light emitting from element 32 cannotbe separated from light bulb 34 that surrounds it. Light element 32radiates in all directions, while reflector 12 concentrates the light tocounteract the spreading. The concentration efficiency of the reflectorto the second focal spot depends upon the design of the reflector aswell as the aperture and ranges from about five to about eighty percentof the total light.

Second focal spot F2 is an enlarged representation of light source 10.The distance of shield 14 and thus aperture 16 from light source 10 canbe within a range and need not place aperture 16 exactly at the positionof second focal spot F2. As used herein “proximate to the second focalspot” is meant to include exactly at second focal spot F2, or withinabout plus or minus twenty percent of the distance between first andsecond focal spots F1 and F2 of second focal spot F2. The specificlocation will vary according to the goals of a system design. Ifaperture 16 is closer to light source 10 than second focal spot F2, awider cone angle will occur past aperture 16. If aperture 16 is fartherfrom light source 10 than second focal spot F2, a smaller cone anglewill occur past aperture 16. The smaller cone angle has less total lightthan the larger cone angle but results in more intense light at thetarget area (that is, higher luminosity). A cone angle is shown in FIG.2, for example, by lines 40 and 42 which are outer portions of an anglerepresenting a total light field, and by lines 36 and 38 which are outerportions of an angle within the total light field representing a desiredlight field.

When selecting the size of aperture 16, a balance occurs between edgecontrast and light throughput. By shrinking the size of aperture 16, theedge contrast is increased at the expense of light throughput.Conversely, by increasing the size of aperture 16, edge contrast isdecreased and light throughput is improved. Typically, in medicalapplications, edge contrast requirements are about 4.5 to about 1 over adistance (of about 6 mm) across the edge with a 1 mm slit or resolution.Edge contrast is measured with a light meter at the bright area which isthen moved into the dark area to obtain the bright/dark ratio inluminosity.

In one embodiment of the present invention, light source 10 comprises ahalogen lamp optimized for long life. Because of inherent tradeoff,halogen lamps with long rated life have significantly lower luminousefficacy than quartz-halogen projector lamps (as much as about 50%). Byusing the long life halogen lamp in conjunction with other aspects ofthe present invention to overcome the lower luminous efficacy,sufficient luminosity can be provided to target area 24.

In a more specific embodiment, the halogen lamp comprises an axiallypositioned filament coil (shown in FIG. 2 as light emitting element 32),and each dimension of the coil is smaller than a corresponding dimensionof aperture 16. For example, coils typically have a length and adiameter. If aperture 16 is a square shape (as shown by aperture 62 ofFIG. 5, for example), both the length and the diameter of the filamentcoil are selected to be smaller than the side of the square. If aperture16 is a circle shape (as shown by aperture 64 of FIG. 6, for example),both the length and the diameter of the filament coil are selected to besmaller than the diameter of the circle. In an even more specificembodiment which has been found to reduce off-axis geometrical errors(due to small filament sizes), the filament coil is wound in a helixhaving a length and a diameter, and the length of the helix is equal toor less than about twice the diameter of the helix.

Another useful parameter when selecting light source 10 is robustness.As used herein, “robust” means sufficiently capable of withstandingrepetitive operation in the intended environment. In the medical X-raymachine environment, for example, a light source is often cyclicallyturned on for about 60 seconds to about 90 seconds and then turned offfor about 60 seconds.

Still another useful parameter when selecting light source 10 is therestart voltage. Halogen lamps, for example, have substantially similar(meaning identical or within plus or minus about 10 percent of eachother) restart and operation voltages. This property is an advantage ascompared with light sources requiring higher restart voltages thanoperational voltages such as HID lamps. In one embodiment, light source10 has a restart voltage equal to or less than about 48 volts. In a morespecific embodiment, the restart voltage is equal to or less than about12 volts. When a halogen lamp is used, the power level is typically in arange of about 35 watts to about 150 watts with the optimal valuedepending upon the filament size and the lumen output.

Yet another useful parameter when selecting light source 10 iscompactness. In a light emitting context, “compact” means that lightemitting element 32 is sufficiently small so that the light fromreflector 12 can be directed at aperture 16. In one embodiment, afilament coil is wound in a helix having a length of about 3.5 mm and adiameter of about 1.7 mm. In a size context, “compact” means that thelight source size does not result in a need for a larger size of thelight system assembly as compared with present light system assemblies.In one example, light bulb 34 is selected to have dimensions with eachbeing about 10 millimeters or less. In a more specific example, lightbulb 34 comprises a cylindrical shape having a diameter of about 1 cmand a length of about 1.3 cm.

Optical concentrator 11 is configured for concentrating X-ray localizerlight from light source 10 to second focal spot F2 with aperture 16being situated proximate to second focal spot F2 and becoming a virtuallight source aligned to the X-ray source. Optical concentrator 11 maycomprise one or more lenses (not shown), one or more reflectors, orcombinations thereof, for example.

In one embodiment, optical concentrator 11 comprises a reflector 12(meaning at least one reflector 12). In a more specific embodiment,light source 10, reflector 12, and shield 14 are configured toconcentrate about 10 percent of total light emitted by the light source10 through aperture 16. The most intense region of the light about focalspot F2 is typically no more than about 5 millimeters (mm) in diameter,so aperture size of about 4 to 5 mm represents the best tradeoff betweenlight throughput and edge contrast.

Reflector 12 typically is a smooth surface reflector comprising athermally conductive material coated by dichroic mirror material.Examples of appropriate thermally conductive materials include glass andaluminum. Dichroic mirror coatings are useful for reflecting visiblelight and transmitting heat.

In one embodiment, reflector 12 comprises a quasi-ellipsoidal portion26, and light source 10 is situated within quasi-ellipsoidal portion 26.In a more specific embodiment, light source 10 is attached to reflector12 with light emitting element 32 centered about first focal spot F1.Quasi-ellipsoidal portion 26 may comprise an elliptical shape or a shapealtered from a pure ellipse to improve concentration of light throughaperture 16 (in other words, a shape designed to follow a certaincurvature). Custom optimization (to accommodate the light source 10which is not a point source) is readily accomplished via commerciallyavailable software tools. In one embodiment, for example, the length (Hin FIG. 1) of quasi-ellipsoidal portion 26 is in the range of about 40mm to about 60 mm, the inner diameter of the quasi-ellipsoidal portion(CA in FIG. 1) ranges from about 45 mm to about 55 mm, and the distancebetween focal spots F1 and F2 ranges from about 54 mm to about 58 mm.

Shield 14 may comprise any structurally suitable opaque material.Mechanically rigid materials that can withstand operating temperaturesare particularly useful. In one embodiment, for example, shield 14comprises aluminum. Although larger thicknesses can be used, a typicalexample range of shield thicknesses is about 0.5 mm to about 2 mm.Aperture 16 may comprise any polygonal shape. As used herein, a“polygonal” aperture may include an aperture having corners (of anydegree) or an aperture having a continuous shape (infinite sides) suchas a round or oblong shape. For X-ray system embodiments whereincollimator 22 (shown in FIG. 1) has a square opening, a square apertureis useful for increasing light intensity at the target area withoutreducing edge contrast. Typically, it is useful to have aperture 16 witha smaller opening facing optical concentrator 11 and a larger openingfacing away from optical concentrator 11 as shown in FIG. 4.

Due to fact that more light reaches aperture 16 from reflector 12 thandirectly from light source 10, the light field emanating from aperture16 is typically darkest in the central region. One way the center can bemade brighter is to diffuse some of the surrounding light into thecenter with an appropriate grade diffuser 60 (shown in FIG. 4) situatedbetween light source 10 and aperture 16.

Positioning diffuser 60 close to aperture 16 is particularly useful forimproving uniformity of light field at target area 24 (shown in FIG. 1).In one embodiment, for example, diffuser 60 is attached directly toshield 14. In a more specific embodiment, an adhesive 58 such as a hightemperature RTV (room temperature vulcanizing) silicone rubber materialis used to maintain the attachment of diffuser 60 to shield 14.

Several examples of useful materials for diffuser 60 include foggy glassand patterned glass. In either of these embodiments, the diffuser isdesigned to disperse light across a predetermined range of angles. Inmedical systems, for example, narrow dispersion angles in the range ofabout twenty degrees or less are typically useful for maximizing usefullight throughput. In one embodiment, the diffuser is square with a sideof about 1 cm long and has a thickness of about 0.2 cm.

The specific embodiments discussed herein can be used in variouscombinations to optimize the needs for a particular light system. In oneexample embodiment, an X-ray localizer light system comprises: a longlife halogen lamp 10; a reflector 12 having first and second focalspots, the lamp being situated at first focal spot F1, reflector 12being configured for concentrating light from the lamp to second focalspot F2; an opaque shield 14 having an aperture 16 therein, aperture 16being situated proximate to second focal spot F2 and being of such ageometrical shape so as to maximize light throughput while meeting lightfield edge contrast requirements of the X-ray localizer system; and adiffuser 60 situated between lamp 10 and aperture 16, wherein thehalogen lamp comprises an axially positioned filament coil and whereineach dimension of the coil is smaller than a corresponding dimension ofaperture 16.

FIG. 3 is a sectional side view of a light system in accordance withanother embodiment of the present invention. The embodiment of FIG. 3 isuseful in the context of X-ray localizer light systems for increasingbrightness in the central region of the light field emanating fromaperture 16 (either in combination with or separately from the diffuserembodiment) but is not intended to be limited to the context of X-raylocalizer light systems. In the embodiment of FIG. 3, reflector 12additionally comprises a cylindrical portion 30 situated betweenquasi-ellipsoidal portion 26 and shield 14 for reflecting stray lightfrom the quasi-ellipsoidal portion in the direction of shield 14, a backreflector portion 44 situated proximate to shield 14, and acentrally-mounted portion 46 situated between the aperture and the lightsource for directing back-reflected light in the direction of aperture16. Proximate to shield 14 means that the back reflector portion issituated on shield 14 or within about 2.5 millimeters from shield 14.Using the embodiment of FIG. 3, part of the light from beyond thequasi-ellipsoidal portion is reflected back toward the end of the lightsource and then in the direction of the aperture to yield more light tothe center portion.

In one embodiment, a transparent cover 48 (comprising a material such asglass, for example) is present between quasi-ellipsoidal portion 26 andcylindrical portion 30, and centrally-mounted portion 46 is attacheddirectly to transparent cover 48. Back reflector portion 44 andcentrally-mounted portion 46 are shaped so as to maximize reflection ofstray light in the direction of aperture 16. In one embodiment, backreflector portion 44 comprises an elliptically curved surface. Severalexamples of back-reflected light are shown by light paths 52 and 54 ofFIG. 3. Using the embodiment of FIG. 3, the light field from aperture 16becomes more uniform.

The description above with respect to the light source, reflector,shield, aperture, and diffuser embodiments of FIGS. 1-2 and 4-6 isequally applicable to the embodiment of FIG. 3.

While only certain features of the invention have been illustrated anddescribed herein, many modifications and changes will occur to thoseskilled in the art. It is, therefore, to be understood that the appendedclaims are intended to cover all such modifications and changes as fallwithin the true spirit of the invention.

What is claimed is:
 1. An X-ray localizer light system comprising: along life X-ray localizer light source; an optical concentrator, thelight source being situated at a first focal spot, the opticalconcentrator being configured for concentrating X-ray localizer lightfrom the light source to a second focal spot; an opaque shield having anaperture therein, the aperture being situated proximate to the secondfocal spot and being of such a geometrical shape so as to maximize lightthroughput while meeting light field edge contrast requirements of theX-ray localizer system.
 2. The system of claim 1 wherein the lightsource comprises a halogen lamp.
 3. The system of claim 2 wherein thehalogen lamp comprises an axially positioned filament coil and whereineach dimension of the coil is smaller than a corresponding dimension ofthe aperture.
 4. The system of claim 3 wherein the filament coil iswound in a helix having a length and a diameter, and wherein the lengthof the helix is equal to or less than about twice the diameter of thehelix.
 5. The system of claim 1 wherein the light source comprises alight source having a rated life of at least about 1000 hours.
 6. Thesystem of claim 5 wherein the rated life is at least about 3000 hours.7. The system of claim 1 wherein the light source comprises a lightsource capable of withstanding repetitive switching operation in anX-ray machine environment.
 8. The system of claim 1 wherein the lightsource comprises a light source having substantially similar restart andoperation voltages.
 9. The system of claim 8 wherein the restart voltageis equal to or less than about 48 volts.
 10. The system of claim 8wherein the restart voltage is equal to or less than about 12 volts. 11.The system of claim 1 wherein the optical concentrator comprises areflector.
 12. The system of claim 11 wherein the reflector comprises aquasi-ellipsoidal portion, and wherein the light source is situatedwithin the quasi-ellipsoidal portion.
 13. The system of claim 12 whereinthe reflector further comprises a cylindrical portion situated betweenthe quasi-ellipsoidal portion and the shield for reflecting stray lightfrom the quasi-ellipsoidal portion in the direction of the shield, aback reflector portion situated proximate to the shield, and acentrally-mounted portion situated between the aperture and the lightsource for directing back-reflected light in the direction of theaperture.
 14. The system of claim 11 wherein the quasi-ellipsoidalportion comprises an elliptical portion.
 15. The system of claim 11wherein the light source, the reflector, and the shield are configuredto provide an efficiency of light from the light source to the aperturein a range of about 10 percent.
 16. The system of claim 11 wherein thereflector comprises a thermally conductive material coated by dichroicmirror material.
 17. The system of claim 1 wherein the shield comprisesaluminum.
 18. The system of claim 1 wherein the aperture comprises asquare aperture.
 19. The system of claim 1 wherein the aperturecomprises a polygonal aperture.
 20. The system of claim 1 furthercomprising a diffuser situated between the light source and theaperture.
 21. The system of claim 20 wherein the diffuser is attached tothe shield.
 22. The system of claim 20 wherein the diffuser comprisesfoggy glass.
 23. The system of claim 20 wherein the diffuser comprisespatterned glass.
 24. An X-ray localizer light system comprising: ahalogen lamp; a reflector having first and second focal spots, the lampbeing situated at the first focal spot, the reflector being configuredfor concentrating light from the lamp to the second focal spot; anopaque shield having an aperture therein, the aperture being situatedproximate to the second focal spot and being of such a geometrical shapeso as to maximize light throughput while meeting light field edgecontrast requirements of the X-ray localizer system; and a diffusersituated between the lamp and the aperture, wherein the halogen lampcomprises an axially positioned filament coil and wherein each dimensionof the coil is smaller than a corresponding dimension of the aperture.25. The system of claim 24 wherein the filament coil is wound in a helixhaving a length and a diameter, and wherein the length of the helix isequal to or less than about twice the diameter of the helix.
 26. Thesystem of claim 24 wherein the reflector comprises an ellipticalportion, and wherein the lamp is situated within the elliptical portion.27. The system of claim 24 wherein the reflector comprises aquasi-ellipsoidal portion, and wherein the lamp is situated within thequasi-ellipsoidal portion.
 28. The system of claim 27 wherein thereflector further comprises a cylindrical portion situated between thequasi-ellipsoidal portion and the shield for reflecting stray light fromthe quasi-ellipsoidal portion in the direction of the shield, a backreflector portion situated proximate to the shield, and acentrally-mounted portion situated between the aperture and the lightsource for directing back-reflected light in the direction of theaperture.
 29. The system of claim 24 wherein the reflector comprises athermally conductive material coated by dichroic mirror material. 30.The system of claim 24 wherein the diffuser is attached to the shield.